Radar, AA, No4 Mk1
Mobile equipment for early warning of aircraft to indicate the approximate range and bearing to equipment radar AA No3 Mk1.
Four-wheeled trailer with steel and wooden cabin for Tx and Rx. Rotatable aerial array
mounted on steel frame-work, collapsible for travelling.
Known as the ZPI (Zone Position Indicator) part of the Canadian GLIII(C) System.
The APF was the No3 Mk1.
Range & Bearing : PPI type (in APF cabin, see Radar, AA, No3 Mk1)
22 rpm radial sweep.
|Wading depth||2'3" still water|
|Towing vehicle||Lorry, 4ton, FWD|
|Operational wavelength||145-155 Mc/s|
|Receiver bandwidth||1Mc/s at -3dB|
|Tx power output||120 kW|
|Tx pulse width||2/4/6 us|
|Recurrence freq||800 to 1200 c/s|
|Detection accuracy||range +/- 1000yds|
|azimuth +/- 2deg|
|Data Transmission||by magslips|
Common T and R.
Horizontal 7-element co-linear array and parasitic reflectors with vertical 6-element array intersparsed.
Open wire feeders.
Turning gear : Aerial array rotated at 22rpm by 3/4 h.p. single phase motor.
115V/230V ac 50c/s or 60c/s, single phase.
Normally supplied by a Cumminss diesel 31 kVA generator.
Technical : 1
PPI operator : 1
Not yet fitted (1944)
Careful siting required for long range and freedom from ground echoes.
Receiver IF signals fed to PPI unit in APF cabin by concentric cable.
References and Sources
- Nomenclature : AA No4 Mk1 (ZPI of GL MkIIIC), 1944.
- R.E.M.E. Museum Archives, Arborfield.
- No1 CRLU Radar History
- Clive Prothero-Brooks, RCA Museum, Shilo, Manitoba, CA
More No4 Mk1 pictures
Production model ZPI trailer showing elliptically polarized antenna. Early model ZPI in the background.
Ten No4 Mk1 radar trailers getting ready for shipment
No4 Mk1 residing at the Royal canadian Artillery Museum, Shilo, Canada.